1. Field of the Invention
A hybrid liquid toner composed of a mixture of two toners, one of which includes an amphipathic molecule composed of various polymeric moieties having different functions at least one of which is a fixing function and another is a dispersant function and a second liquid toner which includes no amphipathic molecule but does include a fixer and a dispersant as separate chemical entities, preferably at least one of the toners including a color agent, and the hybrid toner further including a charge director, and an organic volatile liquid carrier solvent of high electrical resistivity.
2. Description of the Prior Art
A conventional prior art liquid toner typically was composed of a volatile organic liquid solvent system of high electrical resistivity in which there were carried several constituents, some being dispersed and others being dispersed or solvated. Exemplificatively, these other constituents were: a thermoplastic fixer, a dispersant, a pigment which frequently was carbon black, and a charge director, all of these being separate chemical entitles. This type of prior art toner will be referred to hereinafter as a "first" liquid toner.
A second type of liquid toner has been proposed in application Ser. No. 810,841 filed Mar. 26, 1969 for LIQUID TONERS, and in application Ser. No. 7253 filed Jan. 30, 1970 for LIQUID TONERS which is a continuation-in-part of application Ser. No. 810,841. This latter liquid toner will hereinafter be referred to as the "second" liquid toner. The second liquid toner was characterized by the presence therein of an amphipathic molecule which has at least one polymeric moiety thereof included a thermoplastic fixer and has at least another polymeric moiety thereof a dispersant so that these two moieties formed part of a single chemical entity which was a complex molecule. The amphipathic molecule could also include as another moiety thereof a color agent or the color agent could be a chemically separate entity in the second liquid toner. Furthermore, the second liquid toner included a charge director which was not part of the amphipathic molecule. Like the first liquid toner, the second liquid toner additionally included a liquid carrier which was a volatile organic solvent system of high electrical resistivity. Of the said one moiety and the said another moiety, at least one is thermoplastic. The said one moiety is soluble in the solvent system and a portion thereof is a fixative and a dispersant. The said another moiety is insoluble in the solvent system and has a particle size between 25 m.mu. and 25.mu., a portion of said another moiety being a fixative. Thereby the second type of liquid toner has a continuous phase constituting the solvent system with the said moiety dissolved therein and a dispersed phase constituting the said another moiety so that the amphipathic molecule acts as a mono-dispersed particle phase, a fixative and a dispersant.
Each of these two liquid toners had certain advantages and each had certain disadvantages, the disadvantages of the second liquid toner being comparatively minor but nevertheless existent. These disadvantages, and particularly the disadvantages of the second liquid toner, were not important factors in the use of the second liquid toner for most electrostatographic purposes such, for instance, as one of the most widespread applications thereof which constituted its employment in an office copying machine. However, the minor disadvantages of the second liquid toner did to some extent hinder its use in connection with the preparation of lithographic masters and of reproductions for microfiche purposes by an electrostatographic process.
Thus, it has been found that where the second liquid toner was used for making a lithographic master, although the master could be used for a large number of runs, for instance over 15,000, when the runs were considerably longer there was a tendency for the electrostatographically deposited image to deteriorate.
Electrostatographic lithographic masters are prepared by electrostatographically depositing a toner either with or without a color agent on a flexible base which is covered with a photoconductor coating that has had formed therein a latent electrostatic image and subsequently is developed by applying a liquid toner thereto. Both the photoconductor coating and the deposited toner image are oleophilic and to render the image and its carrier useful as a master the background areas having no deposits thereon must be rendered oleophobic which is accomplished by making them hydrophilic. This transformation is effected by a swabbing technique which, for example, employs a water solution of ferrocyanide or ferricyanide as an etchant that attacks the portion of the photoconductor coating which does not bear the electrostatographically deposited image. The photoconductor conventionally used in this technique is zinc oxide in a resin binder, this being a commercial electrostatographic paper.
In connection with the preparation of lithographic masters (as well as for general purposes) with the use of the first liquid toner, a serious disadvantage was present which occurred where the original to be reproduced contained one or more colored (non-white) areas of appreciable size, for instance in excess of one-fourth inch in any dimension. In such cases there was a marked tendency for the deposit of toner on the area to be of greater density adjacent the periphery than at the center. This drawback did not attend the use of the second liquid toner.
As to electrostatographic microfiche reproductions there was a minor disadvantage accompanying the use of the second liquid toner which was that there was a tendency, which might be caused by the large size of the complex molecule, for the boundary line of the image to waver slightly, i.e. to deviate slightly and almost unnoticeably from a faithful reproduction of the boundary line of the original. This disadvantage affected the ability to form a good enlargement of the microfiche image.
A far more serious disadvantage associated with the use of electrostatographic reproduction of microfiche images and which was inherent in the use of the first liquid toner was the difficulty in fixing the electrostatographically deposited image on the carrier. The carrier included a transparent thermoplastic film-forming material containing a transparent photoconductor which was utilized to form the latent electrostatic image, the same subsequently being developed. One such photoconductor which was widely used was a poly-N-vinyl carbazole. After the image had been deposited it had to be fixed. This fixing was accomplished by heating, but, since the film-forming material tended to become dimensionally unstable at approximately the temperature employed for fusing the image, there was a marked tendency for the image to distort which was unacceptable for microfiche uses.